racemic-8,8'-Bis(diphenylphosphino)-3,3',4,4'-tetrahydro-4,4,4',4',6,6'-hexamethyl-2,2'-spirobi[2H-1-benzopyran]

A binucleating diphosphine ligand used as a trans-spanning ligand which rigidly links mutually trans coordination sites via phosphorous atoms separated by a large distance to form a cavity over the face of square planar mono and di-metallic complexes, e.g. in MCl2(SPANphos) (M = Pd, Pt), Rh2(µ-Cl)2(CO)2(SPANphos), the latter useful in, for example, the homogeneous catalytic carbonylation of methanol to acetic acid.